Evaluation of thallium rate in soil after dispersive liquid-liquid micro-extraction

Thallium is widely found in nature, but the only inorganic stones full of this element are crookesite and lorandit. It is also found in pyrites of copper, lead and inorganic stones. The element and its compositions are toxic and harmful to the environment; therefore, its application requires caution and further research. It is important to develop sensitive and accurate analytical methods to determine trace levels of thallium in environmental and real samples. In this research, dispersive liquid-liquid microextraction based on solidification of floating organic drop as a sample preparation method was used for separation and preconcentration of ultra-trace amounts of thallium in soil samples prior to graphite-furnace atomic-absorption spectrometry. Investigated effective parameters on extraction include pH, the amount of chelating agent, type and volume of extraction solvent and extraction time. Under optimum conditions, the calibration curve was linear in the range of 0.2-10.0 ng mL−1 of thallium in the original solution, with limit of detection of 0.03 ng mL−1. The relative standard deviation (RSD) for ten replicated determinations of thallium ion at 5.0 ng mL−1 concentration level was calculated as 3.3%. The proposed method was successfully applied to the determination of thallium in soil samples.